The present invention relates to thermoplastic, moldable, non-exuding phase change materials and method of making same.
Phase change materials may be repeatedly converted between solid and liquid phases and utilize their latent heat of fusion to absorb, store and release heat or cool during such phase conversions.
These latent heats of fusion are greater than the sensible heat capacities of the materials. For example, in phase change materials, the amount of energy absorbed upon melting or released upon freezing is much greater than the amount of energy absorbed or released upon increasing or decreasing the temperature of the material over an increment of 10.degree. C.
Upon melting and freezing, per unit weight, a phase change material absorbs and releases substantially more energy than a sensible heat storage material that is heated or cooled over the same temperature range. In contrast to a sensible heat storage material that absorbs and releases energy essentially uniformly over a broad temperature range, a phase change material absorbs and releases a large quantity of energy in the vicinity of its melting/freezing point.
The problem with such phase change materials is in containing them in an appropriate matrix. In my U.S. Pat. No. 5,053,446, there is disclosed a polyolefin matrix containment system; in my U.S. Pat. No. 4,797,160, there is disclosed use of a cementitious matrix containing alkyl hydrocarbon phase change materials neat or in pellets or granules formed by incorporating the alkyl hydrocarbon phase change material in polymers or rubbers, and in my U.S. Pat. No. 5,106,520 and 5,282,994, there is disclosed a free flowing, conformable powder-like mix of silica particles and a phase change material.
Each of these containment means have properties and utilities for specific applications, but none is universally best for all applications. For example, pellets of a phase change material, such as a crystalline alkyl hydrocarbon, and a polyolefin, such as cross-linked high density polyethylene (HDPE), have been used in floor panels and elsewhere for moderating room temperatures and for energy efficiency. But, such pellets are expensive and have a problem with some "oozing" (exuding) of the low melting point phase change material during thermocycling of the pellets above and below the melting temperature of the phase change material.
Accordingly, it would be desirable to have ways to contain alkyl hydrocarbon phase change materials that might be lower in cost and eliminate oozing and/or provide properties that would enable the phase change material to be more effectively utilized.